1. Field of the Invention
The present invention relates to an image forming apparatus like a copying machine, a printer, a fax machine, or a plotter, each of which has a sheet feeding device.
2. Description of the Related Art
A sheet feeding device, with which a conventional image forming apparatus is equipped, has generally includes a sheet feeding roller that feeds a sheet from a sheet feeding tray, and a conveying roller that is located at a downstream of the sheet feeding roller and conveys the sheet to a registration roller. As a driving unit, one motor has driven a plurality of motors such as the sheet feeding roller, the conveying roller.
At this time, in a conventional technology, a method has been generally proposed where turning on and off an electromagnetic clutch makes each roller perform a different motion to maintain a sheet conveying ability like a control between the sheets, prevention of feeding the sheets while superimposing the sheets, or a jam. The conventional technology has been disclosed, for example, in Japanese Patent Application Laid-open No. 2003-176045 (hereinafter, “Patent document 1”) and in Japanese Patent No. 3782721 (hereinafter, “Patent document 2”).
In Patent document 1, the sheet feeding roller and the conveying roller receive a driving force from the same motor to control a timing of turning on and off each electromagnetic clutch thereof, thereby obtaining the sheet conveying ability.
However, a decline of durability causes many defects where a slide occurs in the electromagnetic clutch, whereby the jam occurs. When a periodic replacement part is removed, a part, which has the highest frequency to be replaced in a market, is the electromagnetic clutch. As a result, a sheet convey, which has depended on turning on and off the electromagnetic clutch, has been configured to lack in reliability.
To solve the problem, Patent document 2 has been proposed the sheet feeding device having employed feed and reverse roller (FRR) (friction separation) method where normal and reverse rotations of the motor are combined with a one-way clutch, whereby the sheet convey is performed without depending on the electromagnetic clutch.
Specifically, the sheet feeding device, which has the sheet feeding roller, the conveying roller, and one motor that drives the rollers at each sheet-feeding stage, is configured in such a manner that the sheet feeding roller and the conveying roller drive in a direction of feeding the sheet when the motor rotates normally, and the conveying roller drives in the direction of feeding the sheet when the motor rotates reversely. At that time, a reverse roller drives in synchronization with the conveying roller.
However, in the technique disclosed in Patent document 2, a reduction ratio of a driving sequence at the time of normal rotation of the conveying roller has been different from the reduction ratio of the driving sequence at the time of reverse rotation of the conveying roller. Therefore, even at a same conveying speed, the motor must have been driven by use of a different pulse at the time of normal rotation compared with the time of reverse rotation, thereby leading to complication of a control table. When the motor is driven by use of the different pulse, a minute speed difference between the time of normal rotation and the time of reverse rotation occurs, thereby resulting in a configuration to cause the sheet conveying ability to be worsened.